Often the headlamp aim of a vehicle headlamp assembly must be adjusted when a headlamp is installed or replaced to ensure that the headlamp light beam provides the optimum night visibility for a given vehicle. Also, for safety reasons, it important to avoid directing the headlamp aim in a direction that may shine directly into the eyes of oncoming traffic. Hence, most headlamp assemblies incorporate a means of adjusting the headlamp aim relative to a given vehicle configuration. In the past, many headlamp assemblies were designed so that the entire headlamp assembly (lens, headlamp, and housing) could tilt for adjustment. However, many modern headlamps have a fixed outer headlamp lens because it is often desirable to have a headlamp assembly that is flush mounted and follows the contours of adjacent vehicle body panels to enhance aerodynamics or styling. In a headlamp assembly with a fixed outer lens, the headlamp typically can tilt within the housing relative to the fixed outer lens for headlamp aim adjustment.
Various adjustment mechanisms for adjusting headlamp aim are well known. Most adjustment mechanisms have an adjustment screw that engages with either the vehicle chassis or the headlamp assembly to push/pull the headlamp actuating a tilt in the headlamp relative to the vehicle chassis or relative to the headlamp assembly in a fixed lens assembly. In the past, the adjustment screw was typically turned by engaging the screw head with a tool directly. For example, many headlamp adjustment mechanisms found on passenger cars and pickup trucks have at least one adjustment screw that has a slot formed in the screw head adapted to receive a phillips-head screwdriver.
For many of the older style headlamp assemblies without a fixed lens, the headlamp aim can be adjusted from outside the vehicle by engaging an adjustment screw head with a screwdriver directly. Some vehicle configurations only provide access to the headlamp adjustment mechanism from within the engine bay, which often requires the hood to be open during adjustment. For the more modern style headlamp assemblies having a fixed outer lens, the headlamp adjustment typically must be accessed from within the engine bay area, from the backside of a body panel, or from underneath a vehicle body panel because the adjustment screw head faces the rear of the vehicle.
But for some applications, it is not feasible to adjust the headlamp aim with the headlamp assembly at its normal operating position while having the hood open. For example, on many heavy trucks the headlamp assembly is mounted to the hood, where the hood is one large integral piece incorporating the front fenders and grill, and the hood tilts forward in its open position about an axis in front of the engine. Thus in such vehicle configurations, the headlamp assembly tilts with the hood and the headlamps are aimed downward when the hood is open. To adjust the headlamp aim, it is typically desirable to have the headlamp aim directed generally horizontal with the headlamp assembly in the same position during adjustment as it would be during normal operation (i.e., with the hood closed). Hence, there is a need for a means of adjusting the headlamp aim for a headlamp assembly with a fixed outer headlamp lens from the exterior of the vehicle, without the need for having vehicle body panels open and without the need to crawl underneath the vehicle to access the adjustment mechanism.